An electrochemical process may be used to recover metals from an impure feed and/or to extract metals from a metal-oxide. A conventional process (for soluble metal oxides) typically involves dissolving a metal-oxide in an electrolyte followed by electrolytic decomposition or (for insoluble metal oxides) selective electrotransport to reduce the metal-oxide to its corresponding metal. Conventional electrochemical processes for reducing insoluble metal-oxides to their corresponding metallic state may employ a single step or multiple-step approach.
A multiple-step approach may be a two-step process that utilizes two separate vessels. For example, the extraction of uranium from the uranium oxide of spent nuclear fuels includes an initial step of reducing the uranium oxide with lithium dissolved in a molten LiCl electrolyte so as to produce uranium metal and Li2O in a first vessel, wherein the Li2O remains dissolved in the molten LiCl electrolyte. The process then involves a subsequent step of electrowinning in a second vessel, wherein the dissolved Li2O in the molten LiCl is electrolytically decomposed to form oxygen and regenerate lithium. Consequently, the resulting uranium metal may be extracted in an electrorefining process, while the molten LiCl with the regenerated lithium may be recycled for use in the reduction step of another batch.
However, a multi-step approach involves a number of engineering complexities, such as issues pertaining to the transfer of molten salt and reductant at high temperatures from one vessel to another. Furthermore, the reduction of oxides in molten salts may be thermodynamically constrained depending on the electrolyte-reductant system. In particular, this thermodynamic constraint will limit the amount of oxides that can be reduced in a given batch. As a result, more frequent transfers of molten electrolyte and reductant will be needed to meet production requirements.
On the other hand, a single-step approach generally involves immersing a metal oxide in a compatible molten electrolyte together with a cathode and anode. By charging the anode and cathode, the metal oxide (which is in electrical contact with the cathode) can be reduced to its corresponding metal through electrolytic conversion and ion exchange through the molten electrolyte. However, although a conventional single-step approach may be less complex than a multi-step approach, the yield of the metallic product is relatively low. Furthermore, the metallic product still contains unwanted impurities.